Study on the Performance of Flat Slab Structure Using Pushover Analysis With and Without Shear Wall

Transcription

1 Study on the Performance of Flat Slab Structure Using Pushover Analysis With and Without Shear Wall Ashwini Ghorpade 1, Dr. B. Shivakumara Swamy 2 1PG Student, Department of Civil Engineering, Dr Ambedkar Institute of Technology, Bangalore, India 2Professor and Head, Department of Civil Engineering, Dr Ambedkar Institute of Technology, Bangalore,India *** Abstract - A three-dimensional RC flat Slab structure (L shape) building is modelled using SAP Flat slab model with and without shear wall and perimeter beams are analysed for earthquake loads using equivalent static method for Z-III and Z-IV and non-linear static method (Pushover Analysis). The results are extracted like displacements, story drifts, torsional moments, member forces, shear wall forces from equivalent static analysis and the pattern of hinge formations, performance points using pushover analysis. The results are compared with all the structural systems of flat slab with and without shear walls and perimeter beams. Addition of shear walls in flat slab structure has a good advantage since there will be significant reduction in displacements and story drifts which are linear and uniform with respect to height and also less compared to flat slab structure without shear walls. From the results and discussions, it can be concluded that, Flat slab structures are preferable in plane of RC structure since displacements and drifts are found to be less for both equivalent static and pushover analysis. Key Words: Displacements, story drifts, hinge formation, performance points, shear wall forces, member forces. 1. INTRODUCTION An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth, which can be violent enough to destroy major structures and kill thousands of people. Earthquake has been known as one of the critical natural disasters for thousands of years. Recent major earthquakes have caused severe social disruption in the territory of the epicenter, especially due to structural failures causing damage to the people and properties. Flat slab is provided in malls, theatres and other structures where large beam, free spaces are required. Shear walls are needed for flat slab construction, when earthquake resistance is considered. Flat slab structures in areas of low seismicity (Zone II) can be designed to resist both vertical and lateral loads as permitted by code IS 1893 Part1:2002. However for areas of high seismicity (Zone III, IV & V) code does not permit flat slab construction without any lateral load resisting system or lateral force resisting system. In this research work, modeling and study of seismic response along with earthquake forces on ten storey (G+9) flat slab multi-storey building in absence and presence of shear wall had been done. Shear wall is placed at core of the building then efficiency and serviceability under Indian standard conditions in seismic zone III & IV been observed for each defined model. Pushover Analysis is a static non-linear analysis and building is subjected to gravity loading. A monotonic displacement controls lateral load pattern which continuously increases through elastic and inelastic behaviour. The initial failures in the building is obtained by the graph of total base shear versus roof displacement (top). The yielding points, crushing and cracks or fractures which are observed in the columns, beams or in any other structural members are obtained. 1.1 OBJECTIVES The basic objective of study on the performance of flat slab structure using pushover analysis with and without shear wall are given below- 1. To analyze a RC flat slab structure for earthquake loads using equivalent static method using IS by considering the effect of shear walls. 2. To understand the hinge formations in columns of flat slab structure using non-linear static (Pushover analysis). 3. To perform earthquake and pushover analysis of flat slab structure with the consideration of perimeter beams and shear wall 4. To evaluate and compare the performance of all the structural system for earthquake and pushover analysis and to find the suitable structural system for flat slab building. 1.2 METHODOLOGY The following method is adopted for the analysis of flab slab to know the performance- 1. A three-dimensional RC flat Slab structure (L shape) building is modelled using SAP Flat slab model with and without shear wall and perimeter beams are analyzed for earthquake loads using equivalent static method (Zone III and Zone IV) and non-linear static method (Pushover). 3. The results are extracted like displacements, story drifts, torsional moments, member forces, shear wall forces from equivalent static analysis. And pattern of hinge formations, performance points using pushover analysis. 4. The results are compared with all the structural systems of flat slab with and without shear walls and perimeter beams. 5. Conclusions are made based on the performance of each system under study. 2018, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 660

2 1.3 BUILDING INFORMATION Structure No. of storey Storey height First storey Upper storey RC Structure G+9 Storey 3.5 m 3.5 m TYPE of building use Commercial Foundation Type Isolated footing / Raft Seismic zone Zone III and Zone IV Assumed Dead Load Intensities Roof finishes 1.50 kn/m 2 Floor finishes 1.50 kn/m 2 Live Load Intensities Roof 3.0 kn/m 2 Floor 3.0 kn/m BUILDING MODELS Modelling Using SAP 2000 These building are modelled with RCC structural elements. Here are the types of model shown for the easy assessment. M-1 M-2 1. MODEL 1 Regular building with RC frame-rc Frame 2. MODEL 2 Regular building with RC frame and shear wall-rc Frame SW 3. MODEL 3 Flat slab structure-flat Slab 4. MODEL 5 Flat slab structure with shear wall-fs SW 5. MODEL 5 Flat slab structure with shear wall and peripheral beam-fs SW-PB The grade of concrete is M-25 and Fe-415. The beam size used are 230x450, 230x600 mm and column size of 230x450 and 230x600mm. The thickness of slab is 175mm, drop is about 325mm and periphery beam is 300X600 mm. M-3 M , IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 661

3 Fig -3: Storey vs. Displacement in Y-Direction M-5 Displacements along X and Y direction in zone III are considerably high in RC frame and flat slab structure. Along X it is found that, flat slab structure has 10% reduced displacements than that of RC structure and 22.3% along Y direction. 2. RESULTS AND DISCUSSIONS For Zone III Fig -4: Storey vs. Storey Drifts in X-Direction Fig -1: Maximum Base Shear Maximum base shear is found to be same for all type of structure as shown in above graph, but comparatively RC frame structure has high base shear of 1129 kn and Flat slab with shear wall structure has lowest base shear of about 13.6% less. Fig -5: Storey vs. Storey Drifts Y-Direction Fig -2: Storey vs. Displacement in X-Direction Storey Drifts are found, maximum in case of RC frame and flat slab structure without shear wall along both X and Y direction, i.e., 5.19 and 4.69 mm along X direction 4.52 and 3.46 mm along Y direction respectively at level 3. Similar to displacements there is significant decrease in Storey Drifts along both X and Y direction with the introduction of shear walls. 2018, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 662

4 For Zone IV Fig -9: Storey vs. Storey Drifts in X-Direction Fig -6: Maximum Base Shear From the above Fig, it can be observed that, due to change in zone from Zone III to Zone IV base force has increased significantly from 1129 kn to 1693 kn which is found to be 33%. Fig -7: Storey vs. Displacements in X-Direction Fig-10: Storey vs. Storey Drifts Y-Direction Like Storey shears, displacements, drifts along X and Y direction has increased with the change in Zone from Zone III to Zone IV. Table-1: Comparison of Different Parameters For Zone III Fig -8: Storey vs. Displacements in Y-Direction Due to change in the earthquake zone from Zone III to Zone IV Storey Displacements are found to be increased 50% along X direction and 58% along Y direction. And similar to Zone III responses presence of shear walls reduced displacements along X and Y direction. Stiffness is given by K=F/δ From the above table, it is observed that the stiffness is maximum for M-5 i.e. Flat slab with shear wall with perimeter beam. When compared with other models. The stiffness increases by 9% for M-5 model when compared to M-2 and also 5% for M-4 when compared to M-2 model. 2018, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 663

5 Table-2: Comparison of Different Parameters For Zone IV Table -3: Comparison of Pushover Analysis Results From the above table, it is observed that the stiffness is maximum for M-4 i.e. Flat slab with shear wall. When compared with other models. The stiffness increases by 5% for M-5 model when compared to M-2 and also 5.6% for M-4 when compared to M-2 model. 2.1 PERFORMANCE POINT: The intersecting point of Demand and Capacity curves is called Performance Point. From the values of Spectural Acceleration(Sa) and Spectural Displacement(Sd) the responses of structures under severe earthquakes are obtained. From the above pushover summary results, it can be observed that, base forces in structures with shear wall are high compared to without shear wall and FSS with shear wall and perimeter beam has high base force along both X and Y direction. Time period at performance point for RC structure is found to more i.e., 3.7 and 3.77 seconds along X and Y direction respectively. Finally displacement at performance point is found to be less in FSS with shear wall i.e., 45 mm and 30 mm along X and Y direction respectively compared to all other structural systems. 3. CONCLUSIONS 1. From the model analysis it can be concluded that, the introduction of shear walls improves more stiffness in the structural systems hence there will be a reduction in time period and increase in the frequency of the structural systems. Introduction of perimeter beams has increased but not significantly. 2. Addition of shear walls in flat slab structure has a good advantage since there will be significant reduction in displacements and also storey drifts are linear and uniform with respect to height and also less compared to flat slab structure without shear walls. Fig -11: Performance Point For M-1 In X-Direction 3. Incorporation of perimeter beams will not have much advantage since there is no considerable reduction in storey drifts and displacements. 4. From the results and discussions, it can be concluded that, Flat slab with shear wall structures are preferable than RC structure since storey displacements and drifts are found to be less for both equivalent static and pushover analysis. SCOPE OF FUTURE WORK 1. The present work can be extended with shear walls at different locations 2. The present study can be extended to high rise structure. Fig -12: Performance Point For M-1 In Y-Direction 2018, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 664

6 REFERENCES [1] Mohamed Abdel-Basset Abdo, Modeling of shear-wall dominant symmetrical flat-plate reinforced concrete buildings. International Journal of Advanced Structural Engineering [2] Kim, H., Lee, D., Kim, C.K. Efficient three-dimensional seismic analysis of a high-rise building structure with shear walls. Engineering Structure 27(6), (2005)[ /pii/s ] [3] Aksogan, O., Bikce, M., Emsen, E., Arslan, H.M., A simplified dynamic analysis of multi-bay stiffened coupled shear walls. Advance Engineering. Software 38, (2007)[ /article/pii/s x] [4] Joseph M. Bracci, Sashi K.Kunnath and Andrei M.Reinhorn. SEISMIC PERFORMANCE AND RETROFIT EVALUATION REINFORCED CONRETE STRUCTURES. - The Indian concrete journal, vol.123 January 1997, pp [5] Patil, K.S.,Gore, N.G.,Salunke, P.J., Optimum design of reinforced concrete flat slab with drop panel, international journal of recent technology and engineering,vol. 2,september international journal of recent technology and engineering,vol. 2,september [11] P. Srinivasulu*, A. Dattatreya Kumar, Behaviour of rcc flat slab structure under earthquake loading International journal of engineering & science research, IJESR/July 2015/ Vol-5/Issue-7/ BIOGRAPHIES Ashwini Ghorpade M.Tech-Structural Engineering Civil Engineering Dr. Ambedkar Institute of Technology Bangalore Dr. B.Shivakumaraswamy Professor and Head, Department of Civil Engineering Dr. Ambedkar Institute of Technology Bangalore [6] P. Srinivasulu*, A. Dattatreya Kumar, Behaviour of rcc flat slab structure under earthquake loading International journal of engineering & science research, IJESR/July 2015/ Vol-5/Issue-7/ [7] Pradip Lande and A. B. Raut, Seismic behavior of flat slab systems, journal of civil engineering and environmental technology, vol. 2.10, pp 7-10, [8] Rajib Kumar Biswas, Md.Meraj Uddin, Md.Arman Chowdhury, Md.Al-Imran Khan, Comparative analysis of a 15 story flat plate building with and without shear wall and diagonal bracing under wind and seismic loads IOSR journal of mechanical and civil engineering (iosr-jmce) e-issn: ,p-issn: x, volume 9, issue 2 (sep. - oct. 2013), pp [9] P. V. Sumanth Chowdary Senthil Pandian. M, A comparative study on rcc structure with and without shear wall ijsrd - international journal for scientific research & development vol. 2, issue 02, 2014 issn (online): [ 2I2328] [10] Patil, K.S.,Gore, N.G.,Salunke, P.J., Optimum design of reinforced concrete flat slab with drop panel, 2018, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 665